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UK Mains Supply Voltages

The electrical supply voltage that powers your critical power, essential and non-essential systems is generated at a high voltage which is then transformed along the UK power distribution network down to the three phase and single phase voltages that you connect to.

The European electrical AC voltages are classified in terms of High Voltage (HV), Medium Voltage (MV) and Low Voltage (LV). The International Electrotechnical Commission has classified the voltages into the following levels (IEC 60038).

Voltage Level Code Voltage Rating
Low Voltage LV up to 1000V
Medium Voltage MV 1000V to 35kV
High Voltage HV 35kV to 230kV
Extra High Voltage above 230kV

The voltage is generated at a high level at source for a number of reasons including losses along the distribution system to the point of use.

UK Single and Three Phase Mains Voltages

In 1995, the supply voltages in Western Europe were harmonised to 230Vac single phase and 400Vac three phase.

Traditional European Harmonised
240Vac 220Vac 230Vac +10% to -6%
415Vac 380Vac 400Vac +10% to -6%

In the UK we can see a wide variation in voltage levels and this is one of the reasons why investment in voltage optimisation can generate energy savings. High mains voltages can reduce power supply long term reliability and low mains voltages can fall outside the input operating voltage window of the power supply leading to a potential power cut and system crash.